Genetics of Blue Tan Coat Color

Yorkies Coat Color Inheritance of Blue Silk Coats

Teaser Yorkies  2003 Cher Hildebrand
What properly bred Yorkies look like.

The Yorkshire Terrier is born Black & Tan (B/T)and should change all black body hair to a dark steel blue as an adult dog. The blue body coat can change color at any time after 8 weeks. I've heard it said that early breakers are always light. I do not find that the case. I have had them break blue by 12 weeks & stay an extremely dark blue all their lives. I have also had later breaking ones go lighter blue than I preferred. The tan is a rich golden tan that keeps darkening with age. The golds seem to keep deepening in color up to about 3 years of age. The Yorkie should always be blue and tan or blue and gold as an adult.

I know there is some confusion, because people assume black is a dominant color in Yorkies. Per Malcolm Willis' "Genetics of the Dog" the genetic makeup is of a B/T dog, which is a recessive color to black, it is not a matter of simple dominant black. B/T is the only gene the Yorkie should be carrying for pattern. The blue coloring is created at another loci. A solid black dog carries the genes AA or A with anything else. The B/T carries a(s)a(s), which is the B/T with a saddle. Anytime an upper case letter is shown that's the dominant & lower case is the recessive. a(s)a(s) shows this as a recessive color. As we go on remember the Yorkie is a B/T dog, but since I will be talking about achieving blue color vs black color, for ease of writing and understanding I will drop off the tan.

The only way a Yorkie can achieve blue color is if they are carrying the Graying gene. Now geneticists refer to it as graying, but in our breed we call the achieved color blue. This is the gene that effects the blue color on breeds that are born one color & turn blue later in life. GG will give you a blue dog and Gg will give you a blue dog, but is carrying the recessive for non blueing and gg will give you a black dog, as this is the non blueing gene. Some confusion comes from people not understanding how they get a black soft coated dog from a breeding of two blue silk dogs. If you are breeding together two dogs that are both Gg then they are both carrying the recessive gene for non blueing and if the two gg genes for non blueing get together it will result in a black dog. When the dog is Gg, the dog will be blue as the dominant gene is G which is what causes the color blue and will exhibit that color. When the dog is gg, the only gene they have is the non blueing gene, so they also can only exhibit that color which will be the black color. Dogs that are born blue carry the dilute gene of dd, which should also not be in the Yorkshire Terrier breed, although that is what would cause the Blue born puppies.

When you breed together two Gg dogs, your chances of mostly blue dogs is very good. Since the dogs in question are blue dogs as they are Gg, G being the dominant and the dogs exhibit that color, but carrying the g which is a recessive they are able to pass that recessive on to the resulting puppies from the mating. The chances of the g sperm from one dog getting with the g egg from the other are not going to be real great but it will occur. Most times the G of one will end up with the g of the other and you still end up with a blue dog. Not to say that the odds are not against you and you end up with a litter of soft coated black puppies. We all know from breeding dogs that nothing holds true 100%.

I know a lot of people breed their black Yorkies, as they feel they have a lot of benefits. This is fine, but I would only breed one to a blue dog. Keep in mind that the blue color is dominant here and the black recessive. A black dog can only throw a recessive gene and if bred to another black dog the resultant puppies will also be black.

An example of a Brussels Griffon litter I had. I bred two rough coated Griffs together. I new the sire had a smooth parent which meant he was carrying the recessive smooth gene. In 6 generations on my girls pedigree there was not a smoothy there and assumed she didn't carry the smooth gene. Low and behold I had 2 smooths out of 3. So this girl was carrying a recessive that has been passed along for atleast 7 generations unseen & finally popped up under the right circumstances.The same can be true of blue silk dogs. You can breed along for many generations assuming you have locked in the color & texture & out pops a black soft coated puppy. The recessives were there hiding within those two parents & finally come together.

Recessive genes are wonderful if they're for the quality you want. In two generations you can totally lock something in your line (such as long hair). The problem can be with dominants, you can breed for it, but you almost always have to continue breeding for it or those little recessives keep sneaking in there. As I mentioned with the Brussels Griffon, they can be passed along for many generations before they actually appear or get the chance to appear.

Density of the shade of blue can be bred for, by selecting dark steel blue whenever possible. This does seem to be a quality that you can lock into with fairly much regularity. As with all the other things in breeding dogs though, when you expect something, always be prepared for something else.

Article printed in TYT Magazine 1999
by author


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